Wheel geometry is very important to the proper operation of a wheeled vehicle, including the handling characteristics of the vehicle. For example, in the case of race cars, wheel geometry may have a tremendous bearing upon the ability of the car to travel quickly around the race course, and thus have an effect upon whether the driver can win the race.
Various devices have been devised for measuring the geometry of wheels of wheeled vehicles. Unfortunately, determining wheel geometry is relatively complex, as are the associated current devices and methods for determining the geometry.
There are several parameters which define wheel geometry. These parameters include toe, caster and camber. The present invention is particularly directed to solving problems associated with determining caster and camber.
The common method of mounting wheels so that they may be turned is to mount the wheel to a pair of ball joints. One joint, the upper ball joint, is mounted above the other ball joint, the lower ball joint. This type of mounting is well-known in the art of motor vehicle wheels.
The upper and lower ball joints need not be mounted in direct vertical alignment. In fact, moving the upper and lower ball joints out of vertical alignment is known to have substantial benefits. The angular departure of the upper and lower ball joints from perfect vertical alignment in a fore and aft direction is called caster. According to convention, caster of a vehicle wheel is negative if the upper ball joint of a vehicle is forward of the lower ball joint, and positive if the upper ball joint is aft of the lower ball joint. The caster of a wheel is measured in degrees and is zero degrees if both upper and lower ball joints reside in a vertical plane. FIG. 1 illustrates “caster” of a vehicle wheel.
As is known, a vehicle wheel with positive caster makes the wheel harder to turn, but results in “automatic steering.” That is, forward motion tends to cause the vehicle wheel to move to the straight-ahead position (i.e. is “self-centering”). Thus, when traveling straight, the wheels tend to stay straight. When coming out of a turn, the wheels tend to move back to the straight position. On the other hand, a vehicle wheel with negative caster turns easily, but may tend to wander, lacking the self-centering effect to maintain the wheel straight.
Camber is the term used to describe the upright orientation of a vehicle wheel measured transversely. The camber of a wheel is measured in degrees and is zero degrees if the wheel resides in a vertical plane perpendicular to the road surface. Camber is negative if the top of the wheel is located inwardly toward the vehicle frame relative to the bottom of the wheel and positive if the top of the vehicle wheel is located outwardly from the bottom of the vehicle wheel relative to the vehicle frame. FIG. 2 illustrates “camber” of a vehicle wheel.
Wheel geometry may be determined by several known, complex procedures. In one embodiment, the wheel or axle spindle (i.e. axle end) upon which the wheel is mounted is exposed. This may require removing a wheel hubcap and spindle cap. Next, a conventional camber-caster gauge is positioned against the exposed end of the wheel spindle so that it bears against the wheel hub, the brake drum or rotor assembly.
The conventional camber-caster gauge is designed to abut the exposed end of the hub or rotor, and a pair of parallel degree gauges, one for measuring caster and one for measuring camber. The two parallel gauges are typically bubble gauges. The inclination of the caster gauge relative to a horizontal orientation can be adjusted.
The measurement of camber is performed with the wheel in exact fore and aft alignment. The camber bubble gauge will thereupon be oriented in a generally horizontal disposition perpendicular to the alignment of the vehicle frame. If the bubble in the bubble gauge rises toward the outboard side of the zero inclination mark of the gauge, a negative camber is indicated. Conversely, if the bubble in the gauge rises toward the inboard end of the gauge, a positive camber is indicated.
The caster bubble gauge is parallel to the camber bubble gauge. Caster is measured by first rotating the wheel so that the spindle is brought 20 degrees to the rear of alignment perpendicular to the orientation of the vehicle frame. The level of the caster bubble is adjusted so that the bubble is precisely at the zero mark on the gauge. The wheel is then turned to bring the spindle precisely 20 degrees forward of perpendicular alignment relative to the alignment of the vehicle frame and the gauge is then leveled. The extent to which the bubble in the caster gauge departs from the zero mark on the gauge is indicative of the caster measurement for that wheel. That is, a rise of the bubble toward the outboard end of the caster gauge will indicated a positive caster, while a migration of the bubble toward the inboard end of the gauge will indicate a negative caster.
To facilitate the turning of the wheels of the vehicle during the caster measuring procedure, it is advantageous to place the wheels upon turntables of a wheel alignment rack or upon portable turntables. This adds to the time and effort, however, of determining the wheel caster.
Corrections in wheel alignments are typically performed by installing eccentrics, shims or moving components in the slots of their attaching points. A combination of these methods may be used to correct the camber and caster settings to pre-defined specifications.
No known existing alignment apparatus achieves or fulfills the purposes of the present invention, namely, to accurately measure vehicle camber and caster without the need to rotate the wheels back 20 degrees, zero the gauge, and then turn the wheels 20 degrees in the other direction to obtain a caster reading. In addition, no known method permits simultaneous determination of camber and caster.